On February 17, 2009 6:35:12 PM -0500 David Magda <dma...@ee.ryerson.ca>
wrote:
On Feb 17, 2009, at 17:56, Joe S wrote:
Does that sound like a viable backup solution?
It has been explicitly stated numerous times that the output of 'zfs
send' has no guarantees and it is undocumented. From zfs(1M):
The format of the [zfs send] stream is evolving. No backwards
compatibility is guaranteed. You may not be able to receive your
streams on future versions of ZFS.
http://docs.sun.com/app/docs/doc/819-2240/zfs-1m
If you want to do back ups of your file system use a documented utility
(tar, cpio, pax, zip, etc.).
I see lots of recent discussion on this and think folks tend to focus
on the wrong part of the problem, which is understandable as the
documentation is only concerned with what is really insignificant
for practical purposes.
If you go to a future version of zfs, simply replace all your "full"
filesystem streams with new ones, and then of course start new
incrementals. Any reasonable backup procedure probably involves starting
new full backups at regular intervals anyway, and more frequently than
you update your filesystem ...
The real problem here is lack of checksums and inability to restore
the good parts of a stream if there is just one bad part. Storing the
stream on zfs would help, but if you can do that you can of course just
receive the stream into a replica filesystem.
There was a lengthy couple of posts within the past couple of weeks on
the merits of tar, cpio, etc. I suggest (to Joe) reading it.
The best way would probably to purchase an external drive and send
updates > to it, then export the drive, and take it offsite.
That's my thoughts as well.
My own take on it is that your backup should be at least as resistant to
bit rot (etc.) as the original filesystem, and when your starting point
is zfs that's a tall order. I guess if zfs itself is not an option for
storing the backups, then someone could add an error correcting checksum
code to the stream (out of band).
-frank
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